<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script>
        function changeImg(){
            var imgObj = document.getElementById("codeImg");
            imgObj.src = "/checkCode?"+Math.random();
        }
    </script>
</head>
<body>
    <form action="login">
        用户名：<input type="text" name="userName"><br>
        密码：<input type="text" name="pwd"><br>
        <img src="/checkCode" id="codeImg">
        <a href="javascript:changeImg()">看不清楚，换一张</a><br>
        请输入验证码：<input type="text" name="code"><br>
        <input type="submit" value="登陆">
    </form>
</body>
</html>